This invention concerns a universal rolling mill stand.
Universal rolling mill stands have the main purpose of producing rolled stock with bent edges and to produce H-beams, I-beams, HIPE sections, etc.
Universal rolling mill stands comprise not only rolls with a horizontal axis but also one or two rolls with a vertical axis positioned respectively either on only one side or on both sides of the rolls with a horizontal axis.
Universal rolling mill stands of the state of the art consist of two monobloc standards connected together at their upper and lower ends by means parallel to the rolls having a horizontal axis.
The chocks which hold the rolls having a horizontal axis and bear the supporting bearings for the rotation of the rolls are positioned between the standards.
The rolls having a vertical axis are installed, instead, on special chocks located between the columns of the standards in an intermediate position between the chocks of the rolls having a horizontal axis.
The rolling mill stands formed in this way are strong, very big and very expensive, entail very long times for changing the rolls and in fact make it impossible to replace the stands themselves quickly. Maintenance work too is complex and takes very long times with considerable plant downtimes.
Rolling mill stands which comprise two pairs of housings anchored to the base plate and acting directly also as vertical guides for the chocks have been proposed to speed up the operations of changing the rolls and of maintenance and to enable the stands to be replaced quickly.
Each pair of housings is associated at its upper and lower ends, by means of two suitable stay bolts, with two cross-heads, a lower cross-head and upper cross-head. These cross-heads can be adjusted towards each other by means of the stay bolts and serve only as a support and abutment for the relative chocks of the rolls having a horizontal axis.
Rolling mill stands of this type entail the drawback that the discharge of the rolling stresses onto the housings causes strains, which may change the trim of the housings and may alter at least the trim of the chocks of the rolls having a horizontal axis owing to the loss of parallelism and alignment that takes place between the guides on which the chocks slide.
These strains are generated by the configuration of the housings and by the type of cooperation obtained between the stay bolts, the housings and the cross-heads.
On the basis of the above, the chocks during working or overloading rest only on one housing and unload thereon all the rolling thrust, while the other housing remains in fact unloaded.
Moreover, the strain generated by the housing under load is translated into a different positioning of the cross-heads, so that the distance between centers of the rolls and, in particular, of the rolls having a horizontal axis is altered and exceeds the tolerance permitted for such processes.
In fact, these strains lead to an alteration of the distance between centers of the upper roll having a horizontal axis and of the lower roll having a horizontal axis.
Furthermore, the rolls having a vertical axis undergo displacements, which are undesirable in themselves and also in relation to the rolls having a horizontal axis and take the processed section out of the permitted tolerance.
Moreover, in the rolling mill stands of the state of the art no devices are included which permit mechanical rough adjustment of the rolls having a vertical axis in combination with a hydraulic system for the continuous adjustment and control of the position of those rolls during the rolling step.